1. Field of the Invention
The present invention relates to a head control device, a storage device, and a maximum power determining method.
2. Description of the Related Art
Data is generally stored in or written to a disk medium in a storage device such as a magnetic disk device or a magneto optical disk device by a head without coming into contact with the disk medium. As the head senses signals produced by a magnet or a laser beam, the sensitivity of the head to the signals increases with the closing of the distance between the head and the disk medium, resulting in increased precision in reading and writing data. With the increasing surface density of the disk medium, the distance between the head and the disk medium, called the floating magnitude, has come to be set to a miniscule value of 10 nanometers or less.
Increasing the minisculeness of the floating magnitude has necessitated a stricter monitoring of fluctuations in the floating magnitude due to variation in the environment. For example, Japanese Patent Application Laid-open No. H11-45436 discloses a technology for monitoring the fluctuations in the floating magnitude by amplitude or jitter amount of signal waveforms generated by the head.
Further, to answer the need for accurately controlling the position of the leading end of the head and to maintain a constant distance between the leading end of the head and the surface of the disk medium (hereinafter, “spacing”), Japanese Patent Application Laid-open No. 2003-272335 has disclosed a technology for adjusting the spacing. In this technology, a heating coil and a thermally-expanding member are provided within the head, and the spacing is adjusted by supplying current to the heating coil and causing the thermally-expanding member to protract, thereby causing the surface of the head facing the magnetic disk to protract towards the magnetic disk. In other words, as shown in FIG. 11, the spacing is adjusted by heating a heater such as a heating coil provided inside a head 100 and causing a head end 102 provided in a data recording/reproducing element 101 to protract towards a magnetic disk 200.
However, if spacing is adjusted by heating the heater, the heater power may become excessive, leading to contact of the head end coming into contact with the surface of the disk medium (hereinafter, “touchdown”), damaging both the head end and the surface of the disk medium and hindering the spinning of the disk medium. In other words, increasing the heater power of the heater causes, as shown in FIG. 12, the head end 102 to touchdown on the surface of the magnetic disk 200. If the heater power continues to be increased after touchdown, due to microscopic unevenness on the surface of the magnetic disk 200, the head end 102 and the surface of the magnetic disk 200 will get damaged as the magnetic disk 200 spins.
Especially, when adjusting the spacing by regulating the heater power, calibration needs to be kept ready so that correspondence relation of the heater power and the spacing can be obtained. For calibration purposes, the heater power has to be increased beyond normal operating conditions and if the heater power is increased excessively, the head end and the disk medium are likely to get damaged under normal operating conditions, leading to error when recording signals to or reading signals from the disk medium.